Determination of 1-β- -arabinofuranosylcytosine and 1-β- -arabinofuranosyluracil in human plasma by high-performance liquid chromatography

A method is described for the determination of 1-β- -arabinofuranosylcytosine (Ara-C) and its metabolite 1-β- -arabinofuranosyluracil (Ara-U) in human plasma. After deproteinization of the plasma sample, separation is performed by reversed-phase liquid chromatography. For Ara-C concentrations exceeding 0.05 mg/l and for Ara-U concentrations exceeding 1 mg/l, injection volumes of 100 μl are applied. For lower concentrations an injection volume of 500 μl is used. Ara-C is detected at 280 nm with a lowest detection limit of 0.002 mg/l in plasma. Ara-U is detected at 264 nm with a lowest detection limit varying from 0.01 to 0.1 mg/l in plasma. This variation is caused by an unknown substance with the same elution properties as Ara-U and which appears to be present in plasma in variable concentrations. The coefficient of variation of the whole procedure is about 6% for Ara-C concentrations above 0.005 mg/l and for Ara-U concentrations above 0.1 mg/l. For lower concentrations the coefficient of variation is about 14%.     

5α,6α-Epoxy-cholestan-3β-ol (cholesterol α-oxide): A specific substrate for rat liver glutathione transferase B

A semi-micro assay was developed for the conjugation of 5α,6α-epoxy-cholestan-3β-ol (cholesterol α-oxide) with glutathione. The soluble supernatant of rat liver homogenate catalysed the reaction at a rate of 0.2–0.5 pmol.min⁻¹ .mg protein⁻¹ with 4μM cholesterol α-oxide, while the reaction in the presence of GSH alone was barely detectable. Enzymic activity in the soluble supernatant was due equally to the two forms of glutathione transferase B (100 pmol.min⁻.mg protein⁻¹), glutathione transferases AA, A, C and E being unreactive. The activity of purified glutathione transferase B was about 5-times that expected from the activity of the soluble supernatant. Complex enzyme kinetics were obtained suggestive of substrate inhibition.     

Chemical synthesis of (1 → 2)-α-D-mannopyranan

The polymerization of 1,2-anhydro-3,4,6-tri-O-benzyl-β-D -mannopyranose proceeds in the presence of Lewis acids, cationic coordination catalysts, and strong bases. Debenzylation of the products yields oligomeric saccharides or low polymers. Polymerization in toluene by means of potassium alkoxide complexed with crown ethers leads to essentially stereoregular (1 → 2)-α-D -mannopyranan. The original derivatives have been characterized by optical rotation, viscosity, molecular weight, gel permeation chromatography, and spectrometry. The free polysaccharides have been characterized by optical rotation, molecular weight, and ¹H- and ¹³C-nmr spectrometry and compared to yeast mannan hydrolysate oligomers.     

MUC1 is a substrate for γ‐secretase

Understanding the underlying mechanisms by which a normal cell avoids the oncogenic potential of MUC1 signaling requires further definition of the pathways by which the MUC1 cytoplasmic tail is processed in both normal and tumor‐derived cells. In the present study we describe the processing pathway initiated by TACE/ADAM17 cleavage of MUC1. Utilizing the human uterine epithelial cell line, HES, derived from normal endometrium, we show that endogenous full length MUC1 undergoes regulated intramembranous proteolysis mediated by presenillin‐dependent γ‐secretase. Cytokine‐stimulated HES cells exposed to γ‐secretase inhibitors accumulated a membrane‐associated 15 kDa fragment of the MUC1 C‐terminal subunit (CTF15). Inhibitors of TACE/ADAM17‐mediated shedding inhibited accumulation of MUC1‐CTF15 and MUC1 ectodomain release to a similar extent consistent with MUC1‐CTF15 being a product of TACE/ADAM17 action. Reduction of catalytically active γ‐secretase complex by nicastrin siRNA treatment also resulted in CTF15 accumulation. Furthermore, mature nicastrin, the substrate receptor for γ‐secretase, co‐immunoprecipitated with CTF15 in the presence of γ‐secretase inhibitors indicating the formation of CTF15: nicastrin complexes. MUC1‐CTF15 accumulation in response to γ‐secretase inhibition was demonstrated in both normal and tumor‐derived cells from humans and mice indicating that this processing pathway exists in many cell contexts. We did not detect products of MUC1 cleavage by γ‐secretase in the presence of various proteasomal inhibitors indicating that subsequent degradation is either non‐proteasomal or extremely efficient. We suggest that this efficient pathway attenuates potential signaling mediated by cytoplasmic tail fragments. J. Cell. Biochem. 108: 802–815, 2009. © 2009 Wiley‐Liss, Inc.     

Changes in levels of mRNAs of transforming growth factor (TGF)-β1, -β2, -β3, TGF-β type II receptor and sulfated glycoprotein-2 during apoptosis of mouse uterine epithelium

To examine the roles played by transforming growth factors (TGF)-β1, -β2, -β3, and TGF-β type II receptors in the induction of apoptosis in the mouse uterine epithelium after estrogen deprivation, we investigated the expression of their mRNAs and the mRNA of sulfated glycoprotein-2 (SGP-2). Pellets containing 100 μg estradiol-17β (E₂) were implanted into ovariectomized mice and removed four days later. Apoptotic indices (percentage of apoptotic cells) of both luminal and glandular epithelia increased after E₂ pellets were removed, but administration of progesterone (P), 5-dihydrotestosterone (DHT), or continued implantation of E₂ pellets suppressed this increase. Levels of mRNAs of TGF-β1, -β2, and -β3, and SGP-2 did not increase after estrogen deprivation. However, estrogen deprivation caused a gradual increase in the level of TGF-β type II receptor mRNA, and its level increased about six-fold six days later. Moreover, E₂, P, and DHT markedly decreased the level of TGF-β type II receptor mRNA. In situ hybridization demonstrated that mRNAs of TGF-β1, -β2, -β3 and TGF-β type II receptor were localized to the epithelium. Exogenous administration of TGF-β1 into the uterine stroma induced apoptosis in the epithelium, a finding that suggests that signals produced by TGF-βs can induce apoptosis. Therefore, the present results suggest that increased sensitivity of uterine epithelial cells to TGF-βs, as demonstrated by an increase in TGF-β type II receptor mRNA, is involved in the induction of apoptosis after estrogen deprivation, although signals produced by TGF-βs do not appear sufficient to induce apoptosis.     

Experimental chiroptical verification of linkage flexibility in methyl 3-O-(α-D-mannopyranosyl)-α-D-mannopyranoside

Vacuum UV CD spectra of methyl 3-O-(α-D -mannopyranosyl)-α-D -mannopyranoside in D₂O and as a cast film were obtained in the 145–200 nM region. The disaccharide solution CD per residue is nearly identical to that of the monosaccharide solution CD, and to the monosaccharide film CD. Conversely, the disaccharide film spectrum exhibits a strong positive CD linkage contribution in the 160–170 nm range, which is consistent with the known crystal conformation under the aegis of previously determined sector rules. The close similarity between the monosaccharide and disaccharide solution spectra, therefore, reflects conformational averaging in which the net linkage contribution is approximately zero. The present observation of significant solution linkage flexibility confirms previous conclusions based on optical rotation, as well as conclusions of others based on nmr data. Moreover, when combined with those earlier results, the present work demonstrates the population of at least three distinct potential energy wells on the disaccharide ϕ, ψ potential energy surface. © 1996 John Wiley & Sons, Inc.     

The role of transforming growth factor-β1, -β2, and -β3 in androgen-responsive growth of NRP-152 rat prostatic epithelial cells

We have investigated the role of autocrine/paracrine TGF-β secretion in the regulation of cell growth by androgens as demonstrated by its inhibition by two androgen response modifiers; the nonsteroidal antiandrogen hydroxyflutamide (OHF), believed to act by inhibiting androgen binding to androgen receptors, or finasteride, an inhibitor of 5α-reductase, the enzyme necessary for the conversion of testosterone to 5α-dihydrotestosterone (DHT), using the nontumorigenic rat prostatic epithelial cell line NRP-152. Growth of these cells was stimulated three- to sixfold over control by either testosterone or DHT under serum-free culture conditions. This was accompanied by a two- to threefold decrease in the secretion rate of TGF-β1, -β2, and -β3. Finasteride reversed the ability of testosterone but not DHT to stimulate growth and downregulate expression of TGF-β1, -β2, and -β3 in a dose-dependent fashion, suggesting that this activity of testosterone required its conversion to DHT. OHF antagonized the stimulatory effects of DHT on NRP-152 cell growth but could reverse the inhibitory effects of DHT only on TGF-β2 and TGF-β3 and not TGF-β1 secretion. This suggests that either TGF-β1 regulation by DHT or the androgen antagonism of OHF occurs independent of androgen receptor binding. Neutralizing antibodies to TGF-β (pantropic and isoform-specific) were able to block the ability of finasteride to antagonize the effects of testosterone nearly completely while only partially inhibiting the antiandrogenic effects of OHF. Thus, the ability of androgens to stimulate growth of NRP-152 cells involves the downregulation of the production of TGF-β1, -β2, and -β3 in addition to other growth-stimulatory mechanisms. J. Cell. Physiol. 175:184–192, 1998. Published 1998 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Characterisation of an associate 17-β-hydroxysteroid dehydrogenase activity and affinity labelling of the 3-α-hydroxysteroid dehydrogenase of Pseudomonas testosteroni

The 3-α-hydroxysteroid dehydrogenase and the 3-β-hydroxysteroid dehydrogenase of Pseudomonas testosteroni were purified to homogeneity by polyacrylamide gel electrophoresis using the following stages: DEAE cellulose chromatography, affinity chromatography on oestrone-aminocaproate sepharose and Sephadex gel filtration.The pure 3-α-hydroxysteroid dehydrogenase was completely devoid of 3-β-hydroxysteroid dehydrogenase activity but could oxidize estradiol 17-β at an appreciable rate. This activity accounts for about 40 per cent of the total 17-β-estradiol dehydrogenase of the crude bacterial extract.Affinity labelling of pure 3-α-hydroxysteroid dehydrogenase was carried out using 5-β-pregnane 3,20-dione-12-α-iodoacetate and 5-α-androstane 3-one-17-β-bromoacetate. With both reagents, inactivation was obtained only in the presence of coenzyme, the substrate protected against inactivation and the enzyme was fully inhibited with covalent binding of 1 mole of reagent per mole of subunit suggesting an active site directed inhibition. Histidine and methionine were identified as the labelled aminoacid residues.     

Synthesis and evaluation of novel daunomycin-phosphate-sulfate -β-glucuronide and -β-glucoside prodrugs for application in adept

The synthesis, antiproliferative effect and enzymatic hydrolysis of daunomycin-3′-N- and -4′-O-phosphate and -sulfate derivatives and of daunomycin-3′-N-CO-β-glucuronide and -β-glucoside, designed to be prodrugs in ADEPT are described. The phosphate derivatives were almost as toxic as the parent drug whereas the sulfates were not hydrolyzed by aryl sulfatases. Glucuronyl and glucosyl prodrugs were found to be useful for application in ADEPT.     

Uneven distribution of protein kinase C-α and -β isozymes in human sarcomas and carcinomas

Protein kinase C (PKC) represents a family of structurally related Ser/Tre kinases which are involved in mitogenic signalling and may contribute to human neoplasia. To address this issue, the messenger RNA and protein levels of PKC isoenzymes α and β were analyzed in several human sarcoma- and carcinoma-derived cell lines. Carcinomas contained low or undetectable levels of either PKC-α or PKC-β. Sarcomas exhibited similar or increased PKC expression compared to human diploid fibroblasts. Moreover, sarcoma cell lines expressing one PKC isoform did not contain detectable levels of the other. When PKC was depleted from the tumor cells, we observed that the PKC overexpressing sarcomas had reduced their malignant properties as determined by their ability to grow in semisolid medium. In addition, epidermal growth factor-stimulated and erbB2-transformed fibroblasts exhibited enhanced cell growth in the absence of PKC. We propose a model for the effect of PKC as a negative regulator of proliferation in epithelial cells and a growth promoter in fibroblasts. © 1994 wiley-Liss, Inc.     

Regulation of steroid 5-α reductase type 2 (Srd5a2) by sterol regulatory element binding proteins and statin

In this study, we show that sterol regulatory element binding proteins (SREBPs) regulate expression of Srd5a2, an enzyme that catalyzes the irreversible conversion of testosterone to dihydroxytestosterone in the male reproductive tract and is highly expressed in androgen-sensitive tissues such as the prostate and skin. We show that Srd5a2 is induced in livers and prostate from mice fed a chow diet supplemented with lovastatin plus ezitimibe (L/E), which increases the activity of nuclear SREBP-2. The three fold increase in Srd5a2 mRNA mediated by L/E treatment was accompanied by the induction of SREBP-2 binding to the Srd5a2 promoter detected by a ChIP–chip assay in liver. We identified a SREBP-2 responsive region within the first 300 upstream bases of the mouse Srd5a2 promoter by co-transfection assays which contain a site that bound SREBP-2 in vitro by an EMSA. Srd5a2 protein was also induced in cells over-expressing SREBP-2 in culture. The induction of Srd5a2 through SREBP-2 provides a mechanistic explanation for why even though statin therapy is effective in reducing cholesterol levels in treating hypercholesterolemia it does not compromise androgen production in clinical studies.     

Engineered cystine knot peptides that bind αvβ3, αvβ5, and α5β1 integrins with low‐nanomolar affinity

There is a critical need for compounds that target cell surface integrin receptors for applications in cancer therapy and diagnosis. We used directed evolution to engineer the Ecballium elaterium trypsin inhibitor (EETI‐II), a knottin peptide from the squash family of protease inhibitors, as a new class of integrin‐binding agents. We generated yeast‐displayed libraries of EETI‐II by substituting its 6‐amino acid trypsin binding loop with 11‐amino acid loops containing the Arg‐Gly‐Asp integrin binding motif and randomized flanking residues. These libraries were screened in a high‐throughput manner by fluorescence‐activated cell sorting to identify mutants that bound to α_vβ₃ integrin. Select peptides were synthesized and were shown to compete for natural ligand binding to integrin receptors expressed on the surface of U87MG glioblastoma cells with half‐maximal inhibitory concentration values of 10–30 nM. Receptor specificity assays demonstrated that engineered knottin peptides bind to both α_vβ₃ and α_vβ₅ integrins with high affinity. Interestingly, we also discovered a peptide that binds with high affinity to α_vβ₃, α_vβ₅, and α₅β₁ integrins. This finding has important clinical implications because all three of these receptors can be coexpressed on tumors. In addition, we showed that engineered knottin peptides inhibit tumor cell adhesion to the extracellular matrix protein vitronectin, and in some cases fibronectin, depending on their integrin binding specificity. Collectively, these data validate EETI‐II as a scaffold for protein engineering, and highlight the development of unique integrin‐binding peptides with potential for translational applications in cancer. Proteins 2009. © 2009 Wiley‐Liss, Inc.     

Mechanism of Inhibition of DNA Synthesis by 1-β-D-Arabinofuranosyl-E-5-(2-Bromovinyl)uracil

The mechanism of the inhibitory action of 1-β-D -arabinofuranosyl-E-5-(2-bromovinyl) uracil triphosphate (BV-araUTP) on DNA synthesis by Escherichia coli DNA polymerase I Klenow fragment was studied. Acting as a chain terminator, BV-araUTP inhibited DNA synthesis by Klenow fragment more effectively than 2′, 3′-dideoxythymidine triphosphate (ddTTP). However, the incorporation sites of BV-araU monophosphate were restricted at consecutive dTMP sequence whereas ddTMP was incorporated at every dTMP site.     

Half-of-sites binding of orotidine 5'-phosphate and alpha-D-5-phosphorylribose 1-diphosphate to orotate phosphoribosyltransferase from Saccharomyces cerevisiae supports a novel variant of the Theorell-Chance mechanism with alternating site catalysis

A ping-pong bi-bi kinetic mechanism ascribed to yeast orotate phosphoribosyltransferase (OPRTase) [Victor, J., Greenberg, L. B., and Sloan, D. L. (1979) J. Biol. Chem. 254, 2647-2655] has been shown to be inoperative [Witte, J. F., Tsou, R., and McClard, R. W. (1999) Arch. Biochem. Biophys. 361, 106-112]. Radiolabeled orotidine 5'-phosphate (OMP), generated in situ from [7-(14)C]-orotate and alpha-d-5-phoshorylribose 1-diphosphate (PRPP), binds tightly enough to OPRTase (a dimer composed of identical subunits) that the complex survives gel-filtration chromatography. When a sample of OMP.OPRTase is extensively dialyzed, a 1:1 (per OPRTase dimer) complex is detected by (31)P NMR. Titration of the apoenzyme with OMP yields a (31)P NMR spectrum with peaks for both free and enzyme-bound OMP when OMP is in excess; the complex maintains an OMP/enzyme ratio of 1:1 even when OMP is in substantial excess. A red shift in the UV spectrum of the OMP.OPRTase complex was exploited to measure K(d(OMP)) = 0.84 muM and to verify the 1:1 binding stoichiometry. PRPP forms a Mg(2+)-dependent 1:1 complex with the enzyme as observed by (31)P NMR. Isothermal titration calorimetry (ITC) experiments revealed 1:1 stoichiometries for both OMP and Mg(2+)-PRPP with OPRTase yielding K(d) values of 0.68 and 10 microM, respectively. The binding of either 1 equiv of OMP or PRPP is mutually exclusive. ITC experiments demonstrate that the binding of OMP is largely driven by increased entropy, suggesting substantial distal disordering of the protein. Analytical gel-filtration chromatography confirms that the OMP.OPRTase complex involves the dimeric form of enzyme. The off rate for release of OMP, determined by magnetization inversion transfer, was determined to be 27 s(-)(1). This off rate is somewhat less than the k(cat) in the biosynthetic direction (about 39 s(-)(1)); thus, the release of OMP from OMP.OPRTase may not be kinetically relevant to the steady-state reaction cycle. The body of available data can be explained in terms of alternating site catalysis with either a classical Theorell-Chance mechanism or, far more likely, a novel "double Theorell-Chance" mechanism unique to alternating site catalysis, leading us to propose co-temporal binding of orotate and the release of diphosphate as well as the binding of PRPP and the release of OMP that occur via ternary complexes in alternating site fashion across the two highly cooperative subunits of the enzyme. This novel "double Theorell-Chance" mechanism yields a steady-state rate equation indistinguishable in form from the observed classical ping-pong bi-bi kinetics.     

Properties of mouse α-galactosidase

α-Galactosidase has been examined in various murine tissues using the substrate 4-methylumbelliferyl-α-galactoside. Mouse liver appears to contain a single major form of the enzyme, as judged by chromatography and electrophoresis. The enzyme was purified 467-fold with a yield of about 40% by a method involving chromatography on Concanavalin A-Sepharose. It has maximal activity at pH 4.2, a K_m value of 1.4 mM, an energy of activation of 16 400 cal/mol, and a molecular weight of 150 000 at pH 5.2. It is inhibited at high concentrations of myoinositol and appears to contain N-acetylneuraminic acid. In these characteristics it resembles human α-galactosidase A.The enzyme from various tissues differs in electrophoretic mobility. After treatment with neuraminidase, however, the enzyme from all tissues comigrates as a single band of activity. By this criterion the α-galactosidase of liver is most heavily sialylated and that from kidney the least. As estimated by gel filtration, the enzyme from liver and kidney exists as species of molecular weight 320 000, 150 000 and 70 000, depending upon pH and ionic strength. This appears to be the result of aggregation of the enzyme, since the forms are interconvertible and under some conditions a single molecular weight species is observed. The liver enzyme is primarily lysosomal, while the kidney enzyme is distributed approximately equally between lysosomal and microsomal fractions.     

Inhibition of mevalonate 5-diphosphate decarboxylase by fluorinated substrate analogs

Mevalonate 5-diphosphate decarboxylase (MDD) is a peroxisomal enzyme in the cholesterol biosynthetic pathway, which plays an important role in regulating cholesterol biosynthesis. In the present study, rat MDD was cloned and purified to apparent homogeneity. Two fluorinated MDD substrate analogs, P'-geranyl 2-fluoromevalonate 5-diphosphate (4) and 2-fluoromevalonate 5-diphosphate (6), were synthesized, and both were found to be irreversible inhibitors of rat MDD. These two inhibitors were characterized, and mechanisms of the inactivation process were proposed. Kinetic studies indicate both analogs only bind into mevalonate binding-site of MDD. Compound 4 shows competitive inhibition on mevalonate kinase (MVK), and its IC(50) value was determined to be comparable with that of geranyl diphosphate. Further kinetic studies indicate compound 4 only bind into ATP binding-site of MVK. These studies provide an example for a single inhibitor to carry out sequential blocking of two enzymes in cholesterol biosynthesis, which may provide useful information for drug discovery for the purpose of treating cardiovascular disease and cancer or for pest control.     

Synthesis of 1-hydroxylated bile acids: Methyl 1α, 3α-dihydroxy 5β-cholan-24-oate

Methyl 1α, 3α-dihydroxy 5β-cholan-24-oate was synthesized to provide a model compound for the mass spectrometric identification of 1α-hydroxylated bile acids.